<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>

	<body>
		<!--
			this 代表自己,就是当前元素
		-->
		<select id="city" onchange="onchangeFn(this)">
			<option value="bj">北京</option>
			<option value="sh">上海</option>
			<option value="sz">深圳</option>
		</select>
		
		
		<script type="text/javascript">
			function onchangeFn(obj) {
				console.log(obj.value)
			}
		</script>

		<!--<script type="text/javascript">
			function onchangeFn() {
				var selectTag = document.getElementById("city")
				console.log(selectTag.value)
			}
		</script>-->
	</body>

</html>